The present invention relates to a method for removing polymer scale deposited on the reactor walls after completion of a polymerization run and a polymer scale remover agent used therefor.
As is known, several different processes are known and practiced in the polymerization of an ethylenically unsaturated monomer or, in particular, vinylic monomer including suspension and emulsion polymerization methods carried out in an aqueous medium, solution polymerization, vapor phase polymerization and bulk polymerization. One of the most serious problems in either one of these polymerization methods is the deposition of polymer scale on the inner walls of the polymerization reactor, stirrer blades and shaft and other surfaces coming into contact with the monomer under polymerization. Deposition of polymer scale is very disadvantageous in several ways that the yield of the polymer product is decreased so much, cooling capacity of the polymerization reactor is reduced due to the poor heat conduction of the scale layer and the quality of the polymer product is degraded due to the possible intermixing of the scale coming off the reactor walls with the product. Therefore, polymer scale deposited on the reactor walls and other parts coming into contact with the monomer should be removed as completely as possible after each polymerization run but such a work for scale removal requires too much labor and time to be economical and, to be worse, involves a further serious problem on the workers' health because polymer scale usually contains a considerably large amount of the unreacted monomer absorbed therein while some of the monomers such as vinyl chloride, acrylonitrile and the like are notoriously toxic to the human body as is a serious public concern in recent years.
Accordingly, several methods have been proposed in which the polymer scale on the reactor walls can be removed without a worker working inside the reactor including a method in which an organic solvent under circulation is sprayed with pressurization at the polymer scale on the reactor walls or the reactor is filled with an organic solvent to dip the polymer scale therein (see, for example, Japanese Patent Publications 46-41366 and 47-19896) and a method in which pressurized water is sprayed at the polymer scale. The methods of using an organic solvent is economically disadvantageous because a quite large volume of the organic solvent is required for the method. In addition, there is a problem of possible pollution of the working environments due to the solvent vapor when an organic solvent at an elevated temperature is used with an object to improve the scale removing effect. The method for the mechanical removal of the polymer scale by use of pressurized water is also disadvantageous because the method is not labor saving requiring a quite long time for complete removal of the polymer scale and the method involves some danger to workers.